Method for Reducing Time of Flight Interference in a Wireless Communication Network

1. A method for identifying time of flight interference in a wireless communication network, the method comprising: detecting interference during a first uplink sub-frame at an interference destination base station; transmitting a time of flight interference source detection request to a gateway, wherein the time of flight interference source detection request comprises a time of flight interference period; determining one or more base stations in the vicinity of the interference destination base station, wherein the one or more base stations in the vicinity of the interference destination base station operate at a same frequency as the interference destination base station; instructing the one or more base stations in the vicinity of the interference destination base station to re-transmit a preamble at least once in a downlink sub-frame; decoding a first preamble of a first interference source base station at the interference destination base station during a second uplink sub-frame; and identifying the first interference source base station based on the first preamble.

2. The method of claim 1 wherein the time of flight interference period comprises a time period of the first uplink sub-frame during which interference is detected.

3. The method of claim 1 further comprising: scheduling no packets during a second uplink sub-frame at the interference destination base station.

4. The method of claim 1 further comprising: decoding a second preamble of a second interference source base station at the interference destination base station during the second uplink sub-frame; and identifying the second interference source base station based on the second preamble.

5. A method for reducing time of flight interference in a wireless communication network, the method comprising: receiving an identification of a first interference source base station and an identification of an interference destination base station; calculating a first time of flight interference period; receiving first source parameters from the first interference source base station; receiving destination parameters from the interference destination base station; calculating a first source time of flight criteria for the first interference source base station based on the first source parameters; calculating a destination time of flight criteria for the interference destination base station based on the destination parameters; transmitting a first source time of flight interference message to the first interference source base station when the first source time of flight criteria is less than or equal to the destination time of flight criteria, wherein the first source time of flight interference message comprises a request to shorten a first source base station downlink sub-frame by at least the first time of flight interference period; and transmitting a destination time of flight interference message to the interference destination base station when the first source time of flight criteria is greater than the destination time of flight criteria, wherein the destination time of flight interference message comprises a request to shorten a destination base station uplink sub-frame by at least the first time of flight interference period, and to delay the start of a destination base station uplink sub-frame by at least the first time of flight interference period.

6. The method of claim 5 wherein calculating a first time of flight interference period comprises: scheduling no data during a second uplink sub-frame at the interference destination base station; and measuring a first interference power and first time of flight interference period during the second uplink sub-frame at the interference destination base station.

7. The method of claim 5 further comprising: transmitting a first source parameter request message to the first interference source base station, wherein the first source parameters are received in response to the first source parameter request message; and transmitting a destination parameter request message to the interference destination base station, wherein the destination parameters are received in response to the destination parameter request message.

8. The method of claim 5 , wherein the first source parameters comprise a first average downlink slot utilization, a first average downlink throughput, first average downlink service flows, and a first average active numbers of users in each class; and wherein the destination parameters comprise an average uplink slot utilization, an average uplink throughput, average uplink service flows, and an average active number of users in each class.

9. The method of claim 8 , wherein the first source time of flight criteria is a weighted sum of the first source parameters; and wherein the destination time of flight criteria is a weighted sum of the destination parameters.

10. The method of claim 5 further comprising: receiving an identification of a second interference source base station; calculating a second time of flight interference period; receiving second source parameters from the second interference source base station; calculating a second time of flight criteria for the second interference source base station based on the second source parameters, wherein the second source time of flight criteria is a weighted sum of the second source parameters; transmitting a first source time of flight interference message to the first interference source base station and a second source time of flight interference message to the second source base station when the sum of the first and second source time of flight criteria is less than or equal to the destination time of flight metric; and transmitting a destination time of flight interference message to the interference destination base station when the sum of the first and second source time of flight criteria is greater than the destination time of flight metric.

11. The method of claim 10 wherein calculating a second time of flight interference period comprises: scheduling no data during a second uplink sub-frame at the interference destination base station; and measuring a second interference power and second time of flight interference period during the second uplink sub-frame at the interference destination base station.

12. The method of claim 10 wherein the second source parameters comprise a second average downlink slot utilization, a second average downlink throughput, second average downlink service flows, and a second average active numbers of users in each class.

13. The method of claim 10 wherein the second source time of flight interference message instructs the second interference source base station to shorten its downlink sub-frames by the second time of flight interference period.

14. The method of claim 10 wherein the destination time of flight interference message instructs the interference destination base station to shorten its uplink sub-frames by the greater of the first and second time of flight interference period, and to delay the start of its uplink sub-frames by the greater of the first and second time of flight interference period.

15. A method for identifying and reducing time of flight interference in a wireless communication network, the method comprising: detecting interference during a first uplink sub-frame at an interference destination base station; transmitting a time of flight interference source detection request to a gateway, including a time of flight interference period comprising a time period of the first uplink sub-frame during which interference is detected; creating a time of flight interference candidates list comprising co-channel base stations in the vicinity of the first base station; instructing all base stations in the time of flight interference candidates list to re-transmit a preamble at least once in a downlink sub-frame; scheduling no packets during a second uplink sub-frame at the interference destination base station; decoding a preamble of an interference source base station at the interference destination base station during the second uplink sub-frame; identifying the interference source base station based on the preamble; measuring an interference power and time of flight interference period during the second uplink sub-frame at the interference destination base station; calculating a source time of flight criteria for the interference source base station; calculating a destination time of flight criteria for the interference destination base station; transmitting a source time of flight interference message to the interference source base station when the source time of flight criteria is less than or equal to the destination time of flight criteria; and transmitting a destination time of flight interference message to the interference destination base station when the source time of flight criteria is greater than the destination time of flight criteria.

16. The method of claim 15 wherein the source time of flight interference message instructs the interference source base station to shorten its downlink sub-frames by the time of flight interference period.

17. The method of claim 15 wherein the destination time of flight interference message instructs the interference destination base station to shorten its uplink sub-frames by the time of flight interference period, and to delay the start of its uplink sub-frames by the time of flight interference period.

18. The method of claim 15 further comprising: transmitting a source parameter request message to the interference source base station; receiving source parameters from the interference source base station in response to the source parameter request message; transmitting a destination parameter request message to the interference destination base station; and receiving destination parameters from the interference destination base station in response to the destination parameter request message.

19. The method of claim 18 , wherein the source parameters comprise an average downlink slot utilization, an average downlink throughput, average downlink service flows, and an average active numbers of users in each class; and wherein the destination parameters comprise an average uplink slot utilization, an average uplink throughput, average uplink service flows, and an average active number of users in each class.

20. The method of claim 19 , wherein the source time of flight criteria is a weighted sum of the source parameters; and wherein the destination time of flight criteria is a weighted sum of the destination parameters.

21. The method of claim 15 wherein creating a time of flight interference candidates list includes calculating the distance between each time of flight interference candidate and the interference source base station, and determining a line of sight between each time of flight interference candidate and the interference source base station.

22. The method of claim 15 further comprising: triggering an alarm if no preamble is decoded during the uplink sub-frame.